Method for monitoring a vibrating gyroscope

ABSTRACT

The invention relates to a method for monitoring a vibrating gyroscope which represents a resonator and forms part of at least one control loop that excites the vibrating gyroscope with its natural frequency by supplying an excitation signal. An output signal can be extracted from the vibrating gyroscope, the excitation signal being derived from said output signal by means of filtering and amplifying. According to the invention, the quality of the resonator is measured. If the measured quality is below a threshold value, an error message is generated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a U.S. national stage of application No. PCT/EP2004/050970,filed on 1 Jun. 2004. Priority is claimed on the following applications:Country: Germany, Application No.: 103 29 508.9, Filed: 30 Jun. 2003.

BACKGROUND OF THE INVENTION

The invention relates to a method for monitoring a vibration gyro, whichrepresents a resonator and is part of at least one control loop whichexcites the vibration gyro by supplying an excitation signal at itsnatural frequency, in which case an output signal can be tapped off fromthe vibration gyro, from which the excitation signal is derived byfiltering and amplification.

By way of example, EP 0 461 761 B1 has disclosed rotation rate sensorsin which a vibration gyro is stimulated on two axes which are alignedradially with respect to a main axis, for which purpose a primary and asecondary control loop are provided, with corresponding transducers, onthe vibration gyro. When rotation rate sensors such as these are used invehicles in order to stabilize the vehicle motion, dangers can occur asa result of failure or a malfunction. In order to prevent this,functional monitoring of the rotation rate sensor is required. Thistakes account of the fact that the vibration gyro is arranged in anevacuated housing in order to achieve the least possible damping, andthat air can enter the housing as a result of ageing or a direct,reducing or precluding the usefulness of the vibration gyro.

In the case of JP 09-218040 A, monitoring such as this is carried our bythe measuring the Q-factor of the resonator and by producing a faultmessage if the Q-factor is below a threshold value. In this case, theQ-factor is measured by switching off the excitation signal and byevaluating the amplitude of the the excitation signal in order toproduce the fault message. The known method is essentially suitable forcarrying out a test when the vehicle is stationary, for example in eachcase after switching on the ignition or during the checking of therotation rate sensor during the course of manufacture.

SUMMARY OF THE INVENTION

The method according to the invention is also suitable for a test duringoperation and comprises an additional phase shift of the excitationsignal being inserted temporarily into the control loop, and anyfrequency change caused by this being evaluated. It depends on theindividual situation whether a temporary phase shift in the excitationsignal or a temporary frequency change will interface with evaluation ofthe rotation rate signal for the respectively intended purpose.

This embodiment is particularly suitable for a digital implementation ofthe control loop, in that, after amplification and analog/digitalconversion, the output signal is demodulated to an in-phase componentand a quadrature component, in that the quadrature component modulates acarrier, after filtering, which carrier is supplied as an excitationsignal to the vibration gyro, in that the in-phase component issupplied, after filtering, to a PLL circuit, which controls thefrequency and the phase of the carrier, in that a signal whichcorresponds to the frequency change is supplied to the PLL circuit inorder to shift the phase of the excitation signal, and causes a phasechange in the carrier.

The invention can preferably be refined in such a way that the phaseshift is approximately 10° with respect to the carrier.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention allows numerous exemplary embodiments. One of these isillustrated schematically in the drawing with reference to a number offigures, and will be described in the following text. In the figures:

FIG. 1 shows a block diagram of a rotation rate sensor,

FIG. 2 shows timing diagrams of signals for the exemplary embodiment,and

FIG. 3 shows block diagram of a rotation rate sensor which is designedto carry out a method according to the exemplary embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The exemplary embodiment as well parts of them are admittedlyillustrated in the form of block diagrams. However, this does not meanthat the arrangement according to the invention is restricted to animplementation with the aid of individual circuits corresponding to theblocks. The arrangement according to the invention can in fact beimplemented in a particularly advantageous manner with the aid oflarge-scale-integrated circuits. In this case, microprocessors can beused which, when suitably programmed, carry out the processing stepsillustrated in the block diagrams.

FIG. 1 shows a block diagram of an arrangement having a vibration gyro 1with two inputs 2, 3 for a primary excitation signal PD and a secondaryexcitation signal SD. Suitable transducers, for example electromagnetictransducers, are used for excitation purposes. The vibration gyro alsohas two outputs 4, 5 for a primary output signal PO and a secondaryoutput signal SO. These signals reflect the respective vibration atspatially offset points on the gyro. Gyro such as these are known, forexample, from EP 0 307 321 A1 and are based on the Coriolis forceeffect.

The vibration gyro 1 represents a high Q-factor filter, with the pathbetween the input 2 and the output 4 being part of a primary controlloop 6, and the path between the input 3 and the output 5 being part ofa secondary control loop 7. The primary control loop 6 is used forexcitation of oscillations at the resonant frequency of the vibrationgyro of, for example, 14 kHz. The excitation in this case is applied onone axis of the vibration gyro, with the oscillation direction that isused for the secondary control loop being offset through 90° withrespect to this. The signal SO is split in the secondary control loop 7into two components, one of which is passed via a filter 8 to an output9, which a signal which is proportional to the rotation rate can betapped off.

A major proportion of the signal processing is carried out in digitalfrom in both control loops 6, 7. The clock signals which are requiredfor signal processing are produced in a crystal-controlled digitalfrequency synthesizer 10, whose clock frequency in the illustratedexample is 14.5 MHz. The application of the method according to theinvention is based primarily on the use of the primary control loop forwhich reason FIG. 3 illustrates one exemplary embodiment of the primarycontrol loop.

In the exemplary embodiment, a switching signal that is shown in FIG. 2a introduces an additional phase shift between the times t1 and t2. Inorder to maintain the resonance conditions, the control loop reacts by achange in the frequency fPO, as is illustrated in FIG. 2 b. In thiscase, if the frequency change exceeds a threshold value S, the Q-factorof the vibration gyro is sufficiently high. If, in contrast, thefrequency change is less, then there is high damping, so that a faultmessage is triggered.

The primary control loop which is illustrated in FIG. 3 has an amplifier11 for the output signal PO, to which an antialiasing filter 12 and ananalog/digital converter 13 are connected. Splitting into an in-phasecomponent and a quadrature component is carried out with the aid ofmultipliers 14, 15, to which carriers Ti1 and Tq1 are supplied. Bothcomponents then pass through a respective (sinx/x) filter 16, 17 and alow-pass filter 18, 19. The filtered real part is supplied to a PIDregulator 20, which controls the digital frequency synthesizer, as aresult of which a phase control circuit is closed, which produces thecorrect phase angle for the carriers Ti1 and Tq1. Furthermore, a carrierTq2 is produced and is modulated in a circuit 22 with the output signalfrom a further PID regulator 21, which receives the low-pass-filteredimaginary part. The output signal from the circuit 22 is supplied to theinput 2 of the vibration gyro 1 as the excitation signal PD.

A microcomputer 23 controls, in addition to other processes, themeasures which are required to carry out the method according to theinvention. For this purpose, the microcomputer 23 passes a signalcorresponding to that shown in FIG. 2 a to the frequency synthesizer,which produces an additional phase shift. The reaction of the phaselocked loop comprises the frequency synthesizer selecting a differentdivision from the clock frequency in order to change the frequency ofthe carriers. This can be supplied as a measure of the frequencydiscrepancy to the microcomputer 23, which then carriers out theevaluation process as explained in conjunction with FIG. 2.

1. A method for monitoring a vibration gyro which represents a resonatorand is part of at least one control loop, the vibration gyro beingexcited by an excitation signal generated by the at least one controlloop at a natural frequency of the vibration gyro, said methodcomprising the steps of: tapping an output signal from which theexcitation signal is derived by filtering and amplification; insertingan additional phase shift of the excitation signal into the at least onecontrol loop; evaluating a Q-factor of the output signal caused by theadditional phase shift; determining whether the Q-factor of thevibration gyro is sufficiently high by the determining whether theQ-factor is above a threshold value; and triggering a fault signal ifthe Q-factor of the vibration gyro is determined to be below thethreshold value, thereby indicating that said Q-factor is insufficientlyhigh.
 2. The method of claim 1, further comprising the steps of:demodulating the output signal to an in-phase component and a quadraturecomponent, after amplification and analog/digital conversion of theoutput signal; modulating, by the quadrature component, a carrier afterfiltering of the quadrature component; supplying the modulated carrieras the excitation signal to the vibration gyro; supplying, afterfiltering, the in-phase component to a PLL circuit that controls thefrequency and phase of the carrier; and supplying a signal correspondingto the frequency change to the PLL circuit to shift the phase of theexcitation signal and cause a phase change in the carrier.
 3. The methodof claim 2, wherein the phase shift with respect to the carrier isapproximately 10°.
 4. The method of claim 1, wherein said step ofevaluating a Q-factor comprises evaluating a frequency change of theoutput signal caused by the additional phase shift.